Settings during refrigerated transport of fruit, expert – course participant conversation

“𝘋𝘦𝘢𝘳 Leo Lukasse, 𝘐 𝘫𝘰𝘪𝘯𝘦𝘥 𝘵𝘩𝘦 𝘤𝘰𝘶𝘳𝘴𝘦 𝘰𝘯 𝘳𝘦𝘧𝘳𝘪𝘨𝘦𝘳𝘢𝘵𝘦𝘥 𝘵𝘳𝘢𝘯𝘴𝘱𝘰𝘳𝘵. 𝘐 𝘸𝘢𝘴 𝘸𝘰𝘯𝘥𝘦𝘳𝘪𝘯𝘨 𝘪𝘧 𝘐 𝘤𝘰𝘶𝘭𝘥 𝘢𝘴𝘬 𝘺𝘰𝘶 𝘧𝘰𝘳 𝘴𝘰𝘮𝘦 𝘢𝘥𝘷𝘪𝘤𝘦, 𝘴𝘪𝘯𝘤𝘦 𝘺𝘰𝘶𝘳 𝘦𝘹𝘱𝘦𝘳𝘵𝘪𝘴𝘦 𝘧𝘢𝘳 𝘴𝘶𝘳𝘱𝘢𝘴𝘴𝘦𝘴 𝘮𝘺 𝘰𝘸𝘯,” starts Georg Tsvetanski, Packhouse Manager at Fruktalina, his mail to professor Lukasse.

Georg: “What conditions need to occur for condensation to form on the fruit? What is the correct procedure for loading a refrigerated truck, if I am to deliver apples at 4-6C? How does the refrigeration unit in the truck react when I load fruit that is of higher temp than the surrounding temp inside the truck? If I need to deliver fruit at 4-6C, what needs to be the temp of the fruit at loading, and what parameters do I set for the refrigeration unit in the truck? If my refrigerated corridor which leads from the cold store to the truck is at 8C is this a problem?”

Leo: “Thanks for your inquiry. Let me give it a try. Though this is one of those moments where I feel that it is too easy to preach simple theories from behind my desk. To transport apples at 1-2C, I would set trailer refrigeration unit at continuous run and supply air temperature control. Return air temperature control is possible, but then make sure to use sufficiently tight top freezing protection settings, if available. Of course it’s nice if apples are properly precooled, but if that’s not the case their temperature will slowly converge to the setpoint or just above it.

Frost exists of white needles. Frozen condense is ice (glassy). How can frost (not ice, but frost!) form on apples? First reduce the apple temperature below 0C, and then bring it in touch with air which has a dewpoint warmer than the apple’s surface temperature. What is ‘air which has a dewpoint warmer than the apple’s surface temperature’? Well, it’s air warmer than the apple, while the air is not exceptionally dry. I hope this helps a little in solving your puzzle.”

More information? Interested in the topic? Reach out to expert Leo Lukasse, Wageningen Food and Biobased Research or visit the (online) course Refrigerated Transport Technology webpage.